Solvatochromic properties of 2,7-carbazole-based conjugated polymers

The solvatochromic properties of poly(N-alkyl-2,7-carbazolediyl)s, poly(N-alkyl-2,7-carbazolediyl-alt-2,5-thiophene)s, poly(N-alkyl-2,7-carbazolediyl-alt-2,5-furan)s, and poly(N-octyl-2,7-carbazoleneethynylene) have been investigated experimentally and theoretically. All polymers have revealed solvatochromic effects, which have been interpreted in terms of the formation of H- and/or J-aggregates. It was observed that the optical properties of the polymers are strongly dependent on the rotational barriers between the subunits present in the polymers. For instance, poly(N-alkyl-2,7-carbazolediyl)s, which possess a relatively high barrier to rotation between adjacent carbazole units, shows a very weak H-band and an intense J-band. On the other hand, poly(N-alkyl-2,7-carbazolediyl-alt-2,5-thiophene)s and poly(N-alkyl-2,7-carbazolediyl-alt-2,5-furan)s, which can reach planarity upon aggregation (low values of torsional barriers), exhibit more intense H-bands. It was also observed that the presence of branched alkyl chains on the nitrogen atom of the carbazole units does not significantly affect the optical properties of the polymers.